start a restructure

Behavioral/Strategy/ComparatorInterface.php

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+<?php
+
+namespace DesignPatterns\Strategy;
+
+/**
+ * Class ComparatorInterface
+ */
+interface ComparatorInterface
+{
+    /**
+     * @param mixed $a
+     * @param mixed $b
+     *
+     * @return bool
+     */
+    public function compare($a, $b);
+}

Behavioral/Strategy/DateComparator.php

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+<?php
+
+namespace DesignPatterns\Strategy;
+
+/**
+ * Class DateComparator
+ */
+class DateComparator implements ComparatorInterface
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function compare($a, $b)
+    {
+        $aDate = strtotime($a['date']);
+        $bDate = strtotime($b['date']);
+
+        if ($aDate == $bDate) {
+            return 0;
+        } else {
+            return $aDate < $bDate ? -1 : 1;
+        }
+    }
+}

Behavioral/Strategy/IdComparator.php

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+<?php
+
+namespace DesignPatterns\Strategy;
+
+/**
+ * Class IdComparator
+ */
+class IdComparator implements ComparatorInterface
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function compare($a, $b)
+    {
+        if ($a['id'] == $b['id']) {
+            return 0;
+        } else {
+            return $a['id'] < $b['id'] ? -1 : 1;
+        }
+    }
+}

Behavioral/Strategy/ObjectCollection.php

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+<?php
+
+namespace DesignPatterns\Strategy;
+
+/**
+ * Class ObjectCollection
+ */
+class ObjectCollection
+{
+    /**
+     * @var array
+     */
+    private $elements;
+
+    /**
+     * @var ComparatorInterface
+     */
+    private $comparator;
+
+    /**
+     * @param array $elements
+     */
+    public function __construct(array $elements = array())
+    {
+        $this->elements = $elements;
+    }
+
+    /**
+     * @return array
+     */
+    public function sort()
+    {
+        if (!$this->comparator){ 
+            throw new \LogicException("Comparator is not set");    
+        }
+        
+        $callback = array($this->comparator, 'compare');
+        uasort($this->elements, $callback);
+
+        return $this->elements;
+    }
+
+    /**
+     * @param ComparatorInterface $comparator
+     *
+     * @return void
+     */
+    public function setComparator(ComparatorInterface $comparator)
+    {
+        $this->comparator = $comparator;
+    }
+}

Behavioral/Strategy/README.md

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+# Strategy
+
+## Terminology:
+
+* Context
+* Strategy
+* Concrete Strategy
+
+## Purpose
+
+To separate strategies and to enable fast switching between them. Also this pattern is a good alternative to inheritance (instead of having an abstract class that is extended).
+
+## Examples
+
+* sorting a list of objects, one strategy by date, the other by id
+* simplify unit testing: e.g. switching between file and in-memory storage

Behavioral/Strategy/index.php

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+<?php
+
+namespace DesignPatterns\Strategy;
+
+$elements = array(
+    array(
+        'id' => 2,
+        'date' => '2011-01-01',
+    ),
+    array(
+        'id' => 1,
+        'date' => '2011-02-01'
+    )
+);
+
+$collection = new ObjectCollection($elements);
+$collection->setComparator(new IdComparator());
+$collection->sort();
+
+$collection->setComparator(new DateComparator());
+$collection->sort();